Three induced mutations of the mouse have resulted in duplications of Beta-globin gene loci. We have studied the globin RNA levels in these mutant animals while the globin DNA structure and globin polypeptide synthesis levels of these mice are under investigation by Dr. R.A. Popp. Two of these mutations have been shown to have normal Beta-/alpha-globin polypeptide levels as well as Beta-/alpha-globin RNA levels in peripheral retriculocytes. These findings are similar to our earlier observations involving alpha-thalassemic mice. In the alpha-thalassemics, abnormal Beta-/alpha-globin gene ratios were not reflected precisely by the mRNA ratios; rather, the RNA ratios were nearer the normal level than were the Beta-/alpha-globin gene ratios. The third type of mouse has been found to have variable Beta-/alpha-globin polypeptide ratios (0.6 to 1.0) but constant Beta-/alpha-globin RNA ratios (0.7). This discrepancy is under further investigation.